1. Field of the Invention
The present invention generally relates to semiconductor power amplifier integrated circuits and, more particularly, is directed to a semiconductor power amplifier integrated circuit suitable for use in a portable telephone terminal.
2. Description of the Related Art
Recently, in land mobile communication such as with a mobile telephone, a portable telephone or the like, a present frequency band allocated to land mobile communication becomes insufficient for radio communication due to an increase in the number of subscribers. Thus, various new services for land mobile communication have been successively started, These new services are common in that they are performed by using digital communication employing a quasi-microwave band of 0.8 to 2 GHz.
At present, the development has been delayed as to microwave integrated circuits such as a monolithic microwave integrated circuit (hereinafter referred to as a MMIC) capable of being used in this frequency band. Terminal devices for such the land mobile communication are indispensable are required to be miniaturized since portability is an important feature the terminal devices. Thus, integration of electric parts used in the terminal device has become a most important problem.
As an example of the related art, there has conventionally been suggested such a semiconductor power amplifier integrated circuit as shown in "Low-Power-Voltage Operated Power Amplification Module", National Conference of the Institute of Electronics, Information and Communication Engineers of Japan, Spring 1993, Paper C-83.
This semiconductor power amplifier integrated circuit uses metal-semiconductor field effect transistors (hereinafter referred to simply as MES FETs) and is integrated in the form of a monolithic microwave integrated circuit (MMIC) up to a drive stage. However, a last stage is provided from the outside as an external part.
As another example of the related art, there is a semiconductor power amplifier integrated circuit as disclosed in "Cellular Telecommunication GaAs Power Module", the Applied Micro-wave, Fall, 1992, pp. 83-88.
Such a semiconductor power amplifier integrated circuit also uses MES FETs and input and output impedance matching circuits thereof are constituted by a distributed constant circuit.
Further, a circuit impedance connected to each of the MES FETs is set in a stable region of each of the MES FETs, respectively.
Since the aforesaid conventional semiconductor power amplifier integrated circuits employ MES FETs each requiring a negative voltage as its gate voltage, these circuits have a major problem in that a negative power source must be employed when the semiconductor power amplifier integrated circuit is applied to a telephone terminal device.
Furthermore, since the circuit impedances connected to the respective MES FETs are required to be set in stable regions of the MES FETs, the degree of freedom upon designing the circuit arrangement is restricted when designing the amplification factor of an amplifier which is sufficiently large.
For this reason, for the purpose of obtaining a necessary amplification factor in such a conventional amplifier, the number of FETs has been increased, which, however, results in an increase of power consumption. Thus, it has been difficult to apply such a conventional amplifier to an apparatus favorably requiring less power consumption such as a portable telephone terminal device.